[CC kvm developers] On Mon, Jul 30, 2012 at 11:45:05AM -0400, Steven Rostedt wrote: > On Tue, 2012-07-24 at 17:07 +0800, Fengguang Wu wrote: > > On Tue, Jul 24, 2012 at 05:03:30PM +0800, Fengguang Wu wrote: > > > And this warning shows up in one of the dozens of boots, for the same > > kconfig. > > > > [ 2.320434] Testing tracer wakeup: PASSED > > [ 2.840288] Testing tracer wakeup_rt: .. no entries found ..FAILED! > > [ 3.280861] ------------[ cut here ]------------ > > [ 3.281967] WARNING: at /c/kernel-tests/src/linux/kernel/trace/trace.c:834 register_tracer+0x1b0/0x270() > > [ 3.284162] Hardware name: Bochs > > [ 3.284933] Modules linked in: > > [ 3.285695] Pid: 1, comm: swapper/0 Not tainted 3.5.0+ #1371 > > [ 3.287032] Call Trace: > > [ 3.287626] [<41035c32>] warn_slowpath_common+0x72/0xa0 > > [ 3.288938] [<410e7dd0>] ? register_tracer+0x1b0/0x270 > > [ 3.290280] [<410e7dd0>] ? register_tracer+0x1b0/0x270 > > [ 3.291516] [<41035c82>] warn_slowpath_null+0x22/0x30 > > [ 3.292723] [<410e7dd0>] register_tracer+0x1b0/0x270 > > [ 3.293921] [<41434c7a>] ? init_irqsoff_tracer+0x11/0x11 > > [ 3.295269] [<41434c95>] init_wakeup_tracer+0x1b/0x1d > > [ 3.296464] [<41001112>] do_one_initcall+0x112/0x160 > > [ 3.297639] [<4141fadd>] kernel_init+0xf7/0x18e > > [ 3.298724] [<4141f455>] ? do_early_param+0x7a/0x7a > > [ 3.299879] [<4141f9e6>] ? start_kernel+0x375/0x375 > > [ 3.301093] [<412b15c2>] kernel_thread_helper+0x6/0x10 > > [ 3.302352] ---[ end trace 57f7151f6a5def05 ]--- > > > > The comment above this test shows: > > * Yes this is slightly racy. It is possible that for some > * strange reason that the RT thread we created, did not > * call schedule for 100ms after doing the completion, > * and we do a wakeup on a task that already is awake. > * But that is extremely unlikely, and the worst thing that > * happens in such a case, is that we disable tracing. > * Honestly, if this race does happen something is horrible > * wrong with the system. > > I guess the question now is, why didn't the RT test wake up? > > Oh wait! You did this on a virt machine. This test isn't designed for > virt machines because the thread could have woken on another vcpu, but > due to scheduling of the host system, it didn't get to run for 100ms, > thus the test will fail because it never recorded the wakeup of the RT > task. > > In other-words, the test is bogus on virt boxes :-/ It's good to quickly get to the root cause :) Can we possibly detect whether we are in a virtual machine and hence skip this particular test case? Thanks, Fengguang -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
